* Inode reflushes (a fsync occuring while the inode is still queued for
a prior fsync) were not ensuring that the inode got pushed to the backend
flusher.

This could lead to deadlocks when the process trying to issue the flush
is the syncer itself.

* The problem typically occured under filesystem loads where a large number
of inodes (aka due to a bulk build) are being flushed at once, and the
flush is unable to finish running before the next syncer cycle comes
around.